Topsheets used in absorbent articles, such as sanitary napkins, are required to have not only absorbing performance for smoothly transferring liquid body waste, e.g., menstrual blood or urine, to an underlying absorbent member but surface characteristics such that the surface thereof in contact with wearer's skin is soft enough not to cause skin irritation.
Currently available topsheets for absorbent articles include nonwoven fabrics made by various processes, perforated nonwoven fabrics, and perforated films of synthetic resins such as polyethylene, but none of them sufficiently satisfies the above-mentioned requirements of absorbing performance and surface characteristics.
Absorbent articles having a topsheet made of nonwoven fabric are disadvantageous in that waste liquid, e.g., menstrual blood or urine, discharged on the topsheet remains in the vicinity of the surface of the topsheet and gives discomfort or an unsanitary impression to a user on account of its color. Absorbent articles having a topsheet made of a perforated film relatively hide the color of blood or urine but are inferior in surface softness to those having a nonwoven fabric topsheet.
Japanese Patent 3131557 discloses wrinkled nonwoven fabric with a great number of streaky wrinkles (ridges) arrayed on its surface, which is used as a topsheet of an absorbent article. However, because of large empty spaces inside the ridges, liquid discharged on the topsheet penetrates into the surface of the wrinkles to make its color noticeable. Besides, this structure is not one that allows the liquid to quickly migrate to the absorbent member, which tends to cause overhydration.
Japanese Patent 3181195 discloses nonwoven fabric suitable for use as a female member of a mechanical fastener of disposable diapers, etc., which is obtained by partly joining a first fiber layer and a second fiber layer by heat fusion and thermally shrinking one of the first and second layers to make the other protrude toward one side to form regularly arrayed bulges. Because the two layers are partly joined by heat embossing in a very fine pattern, the nonwoven fabric is too hard for use as a topsheet of an absorbent article. Further, the fiber layer forming the bulges easily fuzzes up because of weak fusion bonds among constituent fibers. Therefore, if used as the topsheet of the absorbent article, the nonwoven fabric excessively irritates the skin to cause skin troubles.
JP-A-10-80445 discloses a topsheet for absorbent articles which comprises two nonwoven fabric layers and has a large number of openings, the two nonwoven fabric layers being joined together at the periphery of the individual openings. The topsheet disclosed may not be necessarily seen as sufficiently infiltratable for transferring liquid from the first layer (on the wearer's side) to the second layer (on the absorbent member side).